For the broadcasting distribution of video and music contents, in order to research a market and to charge a contents use fee, broadcasts are monitored, and the time and the duration of contents broadcasts are examined. In this type of broadcast monitoring, which uses a specific method, contents identification information is added to broadcast contents and is detected during the broadcasting process. Thereafter, for the contents, the broadcast time and the duration are specified.
Conventional methods for adding identification information to contents include, for example, a method whereby a signal for a special waveform is simply added at the beginning and the end of contents, and a method whereby predetermined information, transported by a sub-carrier, is added at the beginning and the end of contents. According to the second method for transporting information using a sub-carrier, the magnitude of the sub-carrier is changed in accordance with the envelopes of the sounds of the speech or music contents that are broadcast, so that, when successful, the relevant information can not be picked up by the ears of a person. In addition, for video contents, a method exists whereby predetermined coded information is added to the area of a single line that is not used for video recording.
A digital watermarking technique has become popular whereby special information is embedded so that it does not affect the quality of contents. Therefore, it has been proposed that identification information (hereinafter referred to as monitoring information) used for broadcast monitoring be embedded in contents for which a digital watermarking technique is used. In this case, a digital watermark in broadcast data is detected that identifies all the broadcast contents, and detected monitoring information is employed to specify the time predetermined contents were broadcast (the location, along a time axis, occupied by the broadcast data) as well as the time the broadcast monitoring was performed.
Compared with a method for adding information to a sub-carrier and a specific contents area, a method for adding the monitoring information to the contents by using the digital watermarking technique has the following merits. Since information can be embedded throughout the contents, information is seldom lost due to the processing or the deterioration of the contents.
Further, since monitoring information can be added to the contents, it is difficult for a third party to process the information, so that the security in place to prevent forgery and alteration of contents is high.